(1) Field of the Invention
The present invention is directed to underwater acoustic sensors. In particular, the present invention is directed to hydrophones in towed arrays for use with underwater vehicles.
(2) Description of the Prior Art
Underwater vehicles currently utilize n-element towed arrays of acoustic pressure hydrophone sensors. Each hydrophone in the towed array has an omni-directional acoustic beam response. When a hydrophone towed array is designed, the linear array demonstrates an axial symmetric beam pattern. Because of this axial symmetric response, a target signal coming from either the left or the right has the same array response. The inability to distinguish between a left or right array response is referred to as the “left-right ambiguity”. An n-element towed array beam pattern is shown in FIG. 1a, where the towed direction is along the x-axis, and the y-axis is at the starboard direction and z-axis is upward.
An acoustic vector sensor, either particle velocity sensor or accelerometer sensor detects the acoustic information from sound wave particle velocity or acceleration. A single acoustic vector sensor demonstrates a cosine beam pattern independent of the sound wave frequency. To resolve the left-right ambiguity, one could form a vector sensor towed array, where all hydrophone elements of the towed array are replaced by vector sensors or combined pressure-vector sensors. However, this approach introduces a higher level of complexity in regard to the design and operation of the towed array. In order to have a successful working array made of all combined vector sensors, the three dimensional orientations for each vector sensor in the array must be known. Instead of forming an n-element vector sensor towed array, what is needed is a means to resolve the left-right ambiguity in towed arrays of hydrophone sensors through the use of a single combined pressure-vector sensor package, where a pressure hydrophone sensor is integrated with an acoustic vector sensor.